1. Field of the Invention
The present invention relates to improvements in bags made from polymeric film and processes for manufacturing polymeric film bags.
2. Description of the Related Art
Polymeric films are used in a variety of applications. For example, polymeric films are used in sheet form for applications such as drop cloths, vapor barriers, and protective covers. Polymeric films can also be converted into plastic bags, which may be used in a myriad of applications. The present invention is particularly useful to trash bags constructed from polymeric film.
Polymeric bags are ubiquitous in modern society and are available in countless combinations of varying capacities, thicknesses, dimensions, and colors. The bags are available for numerous applications including typical consumer applications such as long-term storage, food storage, and trash collection. Like many other consumer products, increased demand and new technology have driven innovations in polymeric bags improving the utility and performance of such bags. The present invention is an innovation of particular relevance to polymeric bags used for trash collection and more particular for larger bags used for the collection of larger debris, such as yard debris.
Polymeric bags are manufactured from polymeric film produced using one of several manufacturing techniques well-known in the art. The two most common methods for manufacture of polymeric films are blown-film extrusion and cast-film extrusion. In blown-film extrusion, the resulting film is tubular while cast-film extrusion produces a generally planar film. The present invention is generally applicable to drawstring trash bags manufactured from a blown-film extrusion process resulting in tubular film stock. Manufacturing methods for the production of bags from a collapsed tube of material are shown in numerous prior art references including, but not limited to, U.S. Pat. Nos. 3,196,757 and 4,624,654, which are hereby incorporated by reference.
In blown film extrusion, polymeric resin is fed into an extruder where an extrusion screw pushes the resin through the extruder. The extrusion screw compresses the resin, heating the resin into a molten state under high pressure. The molten, pressurized resin is fed through a blown film extrusion die having an annular opening. As the molten material is pushed into and through the extrusion die, a polymeric film tube emerges from the outlet of the extrusion die.
The polymeric film tube is blown or expanded to a larger diameter by providing a volume of air within the interior of the polymeric film tube. The combination of the volume of air and the polymeric film tube is commonly referred to as a bubble between the extrusion die and a set of nip rollers. As the polymeric film tube cools travelling upward toward the nip rollers, the polymeric film tube solidifies from a molten state to a solid state after it expands to its final diameter and thickness. Once the polymeric film tube is completely solidified, it passes through the set of nip rollers and is collapsed into a collapsed polymeric tube, also referred to as a collapsed bubble.
One common method of manufacturing trash bags involves segregating the collapsed polymeric tube into individual trash bags by forming seals which extend transversely across the entire width of the tube. Typically, a line of perforations is formed immediately adjacent and parallel to each seal to facilitate separation of the trash bags one from another. After the trash bags are sealed and perforated, the trash bags can be twice-folded axially into a fractional width configuration.
It is also known to provide wave-cut trash bags. A wave-cut trash bag has a wave or lobe-shaped configuration at its open end. This provides two or more lobes, which can be used to tie the trash bag in a closed configuration after it is filled with refuse.
Wave-cut trash bags can be manufactured by providing closely spaced, parallel transversely extending seals at predetermined intervals along the collapsed polymeric tube. A transversely extending line of perforations is provided between the closely spaced, parallel seals. The collapsed polymeric tube is then separated longitudinally along a wave or lobe-shaped line located equidistant between the edges of the tube.
The lobe-shaped features, or lobes, of a wave-cut trash bags, which may also be referred to as tie-flaps, provide a convenient user feature to tie and close the opening of the bag. The lobes are grasped and knotted to seal the bag opening. Representatives of wave-cut or “tie bags” can be found in the following prior art of U.S. Pat. Nos. 4,890,736, 5,041,317, 5,246,110, 5,683,340, 5,611,627, 5,709,641, and 6,565,794, which are hereby incorporated by reference into this disclosure.
In a further publication, U.S. Pat. Appl. Pub. 2008/0292222A1 discloses a bag having at least two “tie flaps” with gripping features embossed on at least one surface of the tie flaps. It is further disclosed that the bag may be formed from a tube of polymeric material. However, the publication further discloses that the gripping feature is formed in a linear fashion along a length of a blown film bubble that is then slit lengthwise in a wave pattern. The bubble is then formed into bags after being collapsed with a collapsed edge forming a bottom of the bag.
It has been determined, however, that the lobes of prior art wave-cut bags are often difficult to grasp and manipulate, especially if the lobes are contaminated with slippery trash contamination such as oil or grease or moist organic contaminants. Furthermore, wave-cut bags are often manufactured with thicker film than other types of trash bags since they often are intended for use with larger and heavier debris, such as yard debris and debris from home improvement projects. These thicker films used on larger wave-cut bags can be as thick as 3 mils and make it challenging for a user to manipulate the lobes of a wave-cut bag into a knot. Hence, it would be desirable to provide a wave-cut bag that has easier to grasp lobes that are also thinner than the rest of the bag. The present invention represents a novel solution to address this need.
It has also been determined that for certain thicknesses of wave-cut trash bags it may be desirable to provide a bag with thicker lobes relative to thinner a central body of the bag. Thicker lobes may provide a perception of strength to a user when handling the bag and provide a bag that forms a more robust closure. The thinner body of the bag allows a manufacturer to provide thicker lobes that are desired by consumers while also using less raw material than would otherwise be required to form a bag with a uniform thickness having the same thickness the area of the bag's lobes.
Additional problems are understood to be inherent with the use of polymeric films in trash bags. For instance, the use of polymeric film presents technical challenges since polymeric film is inherently soft and flexible. Specifically, all polymeric films are susceptible to puncture and tear propagation. In some instances, it may be possible to increase the thickness of the film or select better polymers to enhance the physical properties of the film. However, these measures increase both the weight and cost of the polymeric film and may not be practicable. In light of the technical challenges of polymeric film, techniques and solutions have been developed to address the need for improved shock absorption to reduce the likelihood of puncture. For example, it is known to impart stretched areas into polymeric films as a means of inducing shock absorption properties into the film.
U.S. Pat. No. 5,205,650, issued to Rasmussen and entitled Tubular Bag with Shock Absorber Band Tube for Making Such Bag, and Method for its Production, discloses using polymeric film material with stretchable zones wherein the film material has been stretched in a particular direction with adjacent un-stretched zones that extend in substantially the same direction. The combination of the stretched zones and adjacent un-stretched zones provides a shock absorber band intended to absorb energy when the bag is dropped. Specifically, when a bag is dropped or moved, the contents inside the bag exert additional forces that would otherwise puncture or penetrate the polymeric film. However, the shock absorber bands absorb some of the energy and may prevent puncture of the film.
Another example of a polymeric film material designed to resist puncture is disclosed in U.S. Pat. No. 5,518,801, issued to Chappell and entitled Web Materials Exhibiting Elastic-Like Behavior. Chappell, in the aforementioned patent and other related patents, discloses using a plurality of ribs to provide stretchable areas in the film much like Rasmussen. Chappell also discloses methods of manufacturing such polymeric film with such ribs.
Another example of shock absorption to prevent puncture is disclosed in U.S. Pat. No. 5,650,214 issued to Anderson and entitled Web Materials Exhibiting Elastic-Like Behavior and Soft Cloth-Like Texture. Anderson discloses using a plurality of embossed ribs defining diamond-shaped areas with a network of unembossed material between the diamond-shaped areas. Thus, the unembossed area comprises a network of straight, linear unembossed material extending in two perpendicular directions.
The foregoing disclosures specifically address the desire to increase the shock absorption of polymeric film to reduce the likelihood of punctures occurring in the film. However, none of the foregoing disclosures address the problem of reducing tear propagation in the polymeric film of a bag.
Previously known solutions to limiting tear propagation are based on two primary concepts. First, longer and more tortuous tear paths consume more energy as the tear propagates and can help in limiting the impact of the tear in a bag or polymeric film. Second, many polymeric films, particularly polymeric films made using a blown-film extrusion process, have different physical properties along different axes of the film. In particular, blown films are known to have higher tear strength in the cross-direction versus the corresponding tear strength in the machine direction. Certain prior art solutions take advantage of the differential properties of polymeric films by redirecting tears into a different direction. This redirecting of tears can offer greater resistance to a tear propagating. For example, some solutions redirect a tear propagating in the weaker machine direction of blown film into the stronger cross-direction.
One solution for reducing tear propagation is based on the idea that longer, tortuous tear paths are preferable and is described in U.S. Pat. No. 6,824,856, issued to Jones and entitled Protective Packaging Sheet. Jones discloses materials suitable for packaging heavy loads by providing an embossed packaging sheet with improved mechanical properties. Specifically, a protective packaging sheet is disclosed where surfaces of the sheet material are provided with protuberances disposed therein with gaps between protuberances. The protuberances are arranged such that straight lines necessarily intersect one or more of the protuberances. The resulting protective packaging sheet provides mechanical properties where tears propagating across the polymeric sheet are subject to a tortuous path. The tortuous path is longer, and more complex, than a straight-line tear, and a tear propagating along such a path would require markedly more energy for continued propagation across the film compared to a tear along a similar non-tortuous path in the same direction. Thus, due to the increased energy required for tear propagation, the tortuous path ultimately reduces the impact of any tears that do propagate across the film.
Another example of a tear resistant plastic film is disclosed in U.S. Pat. No. 8,357,440, issued to Hall and entitled Apparatus and Method for Enhanced Tear Resistance Plastic Sheets. Hall discloses an alternative tortuous path solution and further relies on the fact discussed above that certain polymer films, particularly polymeric films made in a blown-film extrusion process, are known to have a stronger resistance to tear in the cross direction when compared to the machine direction.
Hall discloses a solution that contemplates using preferably shaped embosses, particularly convex shaped embosses with a curved outer boundary, to provide maximum resistance to tear propagation. In most polymeric films, a tear will have a tendency to propagate along the path of least resistance or in the machine direction. Hall contemplates redirecting propagating tears in a tortuous path with the additional intent of redirecting the machine direction tears along the curved edges of the embossed regions and into a cross direction orientation. The redirected tears in the cross direction will be subject to additional resistance and, preferably, will propagate to a lesser degree than a tear propagating in the machine direction in an unembossed film.
U.S. Pat. No. 9,290,303 to Brad A. Cobler (the Cobler patent) with a filing date of Oct. 24, 2013, herein incorporated by reference into this disclosure, discloses use of an embossing pattern on polymeric film that balances both properties of shock absorption and tortuous tear paths in the cross direction, into a single, practicable polymeric film. The patent discloses that the embossing pattern comprises a plurality of embossed regions comprised of a plurality of parallel, linear embosses. The plurality of embossed regions is arranged so that a straight line cannot traverse the polymeric film without intersection at least one of the plurality of embossed regions.
It would be desirable to provide the polymeric film of the body of wave-cut trash bags, or the body of trash bags in general, with the embossing pattern of the Cobler patent. A bag with this pattern would provide a trash bag with improved shock absorption and resistance to tear propagation in comparison to the state of the art wave-cut trash bags. It would also be desirable to provide a wave-cut bag with the Cobler embossing pattern only in the body of the bag and not in the bottom area of the bag or in the lobes of the wave-cut opening. The emboss pattern defined only in the body of the bag would provide the above-discussed advantages without the embossing pattern interfering with the tying of the bag with the lobes or interfering with the bottom seal of the bag. The present invention addresses these additional objectives.